The luminosity functions of E/S0 galaxies are constructed in three different redshift bins (0.2 < z < 0.55, 0.55 < z< 0.8, 0.8 < z < 1.2), using the data from the Hubble Space Telescope (HST) Medium Deep Survey and other HST surveys. These independent luminosity functions show the brightening in the luminosity of E/SOs by about 0.5-1 mag at z ～ 1 and no sign of significant number evolution. This is the first direct measurement of the luminosity evolution of E/S0 galaxies, and our results support the hypothesis of a high redshift of formation (z > 1) for elliptical galaxies, together with weak evolution of the major merger rate at z < 1.
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